U.S. patent number 10,181,619 [Application Number 14/496,506] was granted by the patent office on 2019-01-15 for method of manufacturing nonaqueous electrolyte secondary battery.
This patent grant is currently assigned to AUTOMOTIVE ENERGY SUPPLY CORPORATION. The grantee listed for this patent is AUTOMOTIVE ENERGY SUPPLY CORPORATION. Invention is credited to Tatsuji Numata, Hidetoshi Tamura, Ippei Waki, Hiroshi Yageta.
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United States Patent |
10,181,619 |
Tamura , et al. |
January 15, 2019 |
Method of manufacturing nonaqueous electrolyte secondary
battery
Abstract
An organic acid included in a nonaqueous electrolyte solution of
a secondary battery is reduced. During preparation of a
film-covered battery 1, the nonaqueous electrolyte solution is
injected into an covering 5 of the film-covered battery 1 having an
electrode including: the electrode active material, the binder, and
the organic acid, the organic acid in the nonaqueous electrolyte
solution is decomposed by electrical charging of a battery until a
voltage level is equal to or above a decomposition voltage of the
organic acid, and the gas that is produced by decomposition is
degassed from the cut portion 6 of the covering 5.
Inventors: |
Tamura; Hidetoshi (Sagamihara,
JP), Waki; Ippei (Machida, JP), Numata;
Tatsuji (Kawasaki, JP), Yageta; Hiroshi (Ebina,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
AUTOMOTIVE ENERGY SUPPLY CORPORATION |
Zama-shi, Kanagawa |
N/A |
JP |
|
|
Assignee: |
AUTOMOTIVE ENERGY SUPPLY
CORPORATION (Zama-shi, JP)
|
Family
ID: |
51628032 |
Appl.
No.: |
14/496,506 |
Filed: |
September 25, 2014 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150089798 A1 |
Apr 2, 2015 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 1, 2013 [JP] |
|
|
2013-206067 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
10/049 (20130101); H01M 10/446 (20130101); H01M
4/139 (20130101); H01M 10/058 (20130101); H01M
10/052 (20130101); H01M 4/0447 (20130101); Y02E
60/10 (20130101); Y10T 29/49108 (20150115) |
Current International
Class: |
H01M
10/058 (20100101); H01M 4/139 (20100101); H01M
10/44 (20060101); H01M 10/052 (20100101); H01M
10/04 (20060101); H01M 4/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
07-254436 |
|
Oct 1995 |
|
JP |
|
09-283181 |
|
Oct 1997 |
|
JP |
|
10-74521 |
|
Mar 1998 |
|
JP |
|
10-334888 |
|
Dec 1998 |
|
JP |
|
2002-246013 |
|
Aug 2002 |
|
JP |
|
2004-006188 |
|
Jan 2004 |
|
JP |
|
2008-262895 |
|
Oct 2008 |
|
JP |
|
WO 2011162090 |
|
Dec 2011 |
|
JP |
|
WO 2013065187 |
|
May 2013 |
|
JP |
|
WO 2014038174 |
|
Mar 2014 |
|
JP |
|
2014116233 |
|
Jun 2014 |
|
JP |
|
Other References
Machine translation of JP 2014-116233 A. cited by examiner .
Machine translation of JP 2002246013. cited by examiner .
Korean Office Action and English translation, dated Jan. 26, 2017,
6 pages. cited by applicant .
Japanese Office Action issued in corresponding Japanese Patent
Application No. 2013-206067 dated May 23, 2017 and its English
machine translation thereof. cited by applicant.
|
Primary Examiner: Jelsma; Jonathan G
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
The invention claimed is:
1. A method of manufacturing a nonaqueous electrolyte laminated
secondary battery, comprising: storing a power generating element
having a positive electrode containing an electrode active
material, a binder, and an organic acid in a covering; injecting a
nonaqueous electrolyte solution into the power generating element;
electrical charging of the power generating element until a voltage
level is equal to or above a decomposition voltage of the organic
acid eluted from the positive electrode into the nonaqueous
electrolyte solution, an amount of the organic acid eluted from the
positive electrode into the nonaqueous electrolyte solution being
from one half to two thirds of a total amount of the organic acid;
degassing a gas that is produced by decomposition of the organic
acid to out of the covering via an opening of a cut portion of the
covering; and re-heat sealing the opening of the cut portion.
2. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 1, wherein the organic acid
included in the nonaqueous electrolyte solution is gasified by
electrochemical decomposition resulting from the electrical
charging of the power generating element.
3. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 1, wherein the organic acid is
represented by a chemical formula of R--COOH, where R represents a
monovalent group.
4. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 3, wherein the monovalent
group comprises a carboxyl group, a methyl group, an ethyl group, a
propyl group, or a butyl group.
5. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 1, wherein the organic acid is
represented by a chemical formula of HOOC--Y--COOH, where Y
represents a divalent group.
6. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 5, wherein the divalent group
comprises a methylene group, an ethylene group, a propylene group,
or a butylene group.
7. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 1, wherein the positive
electrode further comprises a positive electrode collector composed
of an electrochemically stabilized metal foil.
8. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 7, wherein the
electrochemically stabilized metal foil comprises an aluminum foil,
an aluminum alloy foil, a copper foil, or a nickel foil.
9. The method of manufacturing the nonaqueous electrolyte laminated
secondary battery according to claim 1, wherein the electrode
active material comprises a lithium manganese complex oxide powder,
a lithium nickel complex oxide powder, or a combination
thereof.
10. The method of manufacturing the nonaqueous electrolyte
laminated secondary battery according to claim 1, wherein the
binder comprises polyvinylidene fluoride,
vinylidenefluoride-hexafluoropropylene copolymer,
vinylidenefluoride-tetrafluoroethylene copolymer, styrene-butadiene
copolymer rubber, polytetrafluoroethylene, polypropylene,
polyethylene, polyimide, or polyamide-imide.
11. The method of manufacturing the nonaqueous electrolyte
laminated secondary battery according to claim 1, wherein the
organic acid comprises oxalic acid.
12. A method of manufacturing a nonaqueous electrolyte laminated
secondary battery, comprising: storing a power generating element
having a positive electrode containing an electrode active
material, a binder, and an organic acid in a covering; injecting a
nonaqueous electrolyte solution into the power generating element;
electrical charging of the power generating element until a voltage
level is equal to or above a decomposition voltage of the organic
acid eluted from the positive electrode into the nonaqueous
electrolyte solution, an amount of the organic acid eluted from the
positive electrode into the nonaqueous electrolyte solution being
from one half to two thirds of a total amount of the organic acid;
and degassing a gas that is produced by decomposition of the
organic acid to out of the covering via an opening of a portion of
the covering; and heat sealing the opening of the portion of the
covering.
Description
TECHNICAL FIELD
The present description relates to a method of manufacturing a
nonaqueous electrolyte secondary battery.
BACKGROUND ART
It is known that at the time a positive electrode active material
layer is formed by coating and drying a slurry (hereinafter,
referred to as "positive electrode slurry") containing a solution
prepared by dispersing a positive electrode material and a binder
in an organic solvent, and kneading and mixing the solution
thereof, an organic acid is added to the organic solvent to prevent
gelation during the preparation of the positive electrode slurry
(see, Patent Literature 1).
SUMMARY OF INVENTION
Technical Problem
It has been determined that an organic acid may elute from a
positive electrode active material layer into a nonaqueous
electrolyte solution during configuration of a secondary battery
that combines the nonaqueous solution or the like with a positive
electrode sheet including the positive electrode active material
layer obtained by application of a positive electrode slurry
containing an organic acid. Organic acid typically receives
electrochemical oxidation-reduction reaction more easily than a
solvent of the nonaqueous electrolyte solution, and thus a
reduction in charge/discharge efficiency of the secondary battery
may result from the oxidation-reduction reaction. In addition, the
abovementioned elution in the positive electrode sheet also applies
to a negative electrode sheet containing the organic acid.
Based on the above, an aim of the present description is to reduce
the organic acid eluted from an electrode of the secondary battery
into the nonaqueous solution.
Solution to Problem
A method of manufacturing a nonaqueous electrolyte secondary
battery of the present description includes storing a power
generating element having an electrode containing an electrode
active material, a binder and an organic acid inside an covering,
injecting the nonaqueous electrolyte solution into the power
generating element, electrical charging of the power generating
element until a voltage level is equal to or above a decomposition
voltage of the organic acid in the nonaqueous electrolyte solution,
and degassing a gas that is produced by decomposition in the
nonaqueous electrolyte solution to out of the covering. According
to the present disclosure, even in cases where the organic acid
included in an original electrode is eluted into the nonaqueous
electrolyte solution, the organic acid is decomposed and eliminated
during the method of manufacturing of the nonaqueous electrolyte
secondary battery.
Advantageous Effects of Invention
A method of manufacturing a nonaqueous electrolyte secondary
battery of the present description includes storing a power
generating element having an electrode containing an electrode
active material, a binder and an organic acid, and a nonaqueous
electrolyte solution inside an covering, injecting the nonaqueous
electrolyte solution into the power generating element, electrical
charging of the power generating element until a voltage level is
equal to or above a decomposition voltage of the organic acid in
the nonaqueous electrolyte solution, and a gas that is produced by
decomposition in the nonaqueous electrolyte solution is degassed to
out of the covering. According to the present disclosure, the
organic acid included in the nonaqueous electrolyte solution in the
method of manufacturing nonaqueous electrolyte secondary battery is
reduced by decomposition and elimination, and thus the
charge/discharge efficiency of the secondary battery is improved at
a time of shipment.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a cross-sectional view of a first embodiment of a
nonaqueous electrolyte secondary battery of a present description;
and
FIG. 2 shows a plan view of a cut portion of an covering of the
nonaqueous electrolyte secondary battery of the present
description.
DESCRIPTION OF EMBODIMENTS
Hereinafter, preferred embodiments of the present invention will be
described.
A film-covered battery 1 of a present embodiment, as indicated in
FIG. 1, is a nonaqueous electrolyte secondary battery including a
nonaqueous electrolyte solution injected into a power generating
element having an electrode active material layer containing an
electrode active material, a binder, and an organic acid.
The film-covered battery 1 is a lithium ion secondary battery, or
the like, which has a flat rectangular outer appearance, as shown
in FIG. 2. The film-covered battery 1 is configured such that a
rectangular-shaped power generating element 4 and the nonaqueous
electrolyte solution are stored inside an covering 5 including a
laminate film. In addition, a positive electrode terminal 2
including a conductive metal foil is disposed at one edge of the
covering 5, and a negative electrode terminal 3 including the same
metal foil is disposed at another edge opposing the one edge.
The power generating element 4 includes alternately laminated
plurality of positive electrode plates 41 and negative electrode
plates 42 separated by separator 43, e.g., three negative electrode
plates 42, two positive electrode plates 41, and four separators 43
disposed therebetween. In the present example, the negative
electrode plate 42 is positioned on both sides of the power
generating element 4. The positive electrode plate 41 may also be
positioned on an outermost layer of the power generating element
4.
The positive electrode plate 41 constitutes a positive electrode
active material layer 41b, 41c on both sides of a
rectangular-shaped positive electrode collector 41a. The positive
electrode collector 41a is composed of an electrochemically
stabilized metal foil, e.g., an aluminum foil, an aluminum alloy
foil, a copper foil, or a nickel foil.
The positive electrode active material layer 41b, 41c is formed by
coating, drying, and rolling a positive electrode slurry formed by
kneading and mixing a positive electrode active material containing
a lithium manganese complex oxide powder and/or a lithium nickel
complex oxide powder, a binder exemplified by polyvinylidene
difluoride (PVDF), an organic solvent exemplified by
N-methyl-2-pyrrolidone, and an organic acid on a main surface of
the positive electrode collector 41a. The lithium manganese complex
oxide and/or lithium nickel complex oxide may be any known complex
oxide used in the lithium ion secondary battery lithium (see,
Patent Literature 1).
In addition to polyvinylidene fluoride, the binder may include
vinylidenefluoride-hexafluoropropylene copolymer,
vinylidenefluoride-tetrafluoroethylene copolymer, styrene-butadiene
copolymer rubber, polytetrafluoroethylene, polypropylene,
polyethylene, polyimide, and polyamide-imide.
It is preferable that the organic acid is electrochemically
decomposed by an electrical charge of the power generating element
or gasified by decarboxylation. Accordingly, almost all or all of a
decomposition by-product of the organic acid may be removed to an
exterior of the covering, and the decomposition by-product of the
organic acid may be removed such that no residual decomposition
by-product remains in the battery. A compound indicated by a
chemical formula (where R represents an optional monovalent group
and Y represents an optional divalent group) such as R--COOH or
HOOC--Y--COOH may be exemplified as the organic acid.
In particular, it is preferable that the R and Y groups in the
compound of the abovementioned chemical formula are each
independently gasified by electrochemical decomposition or
decarboxylation, as the organic acid. The R group may be
exemplified by a carboxyl group, a methyl group, an ethyl group, a
propyl group, and a butyl group. The Y group may be exemplified by
a methylene group, an ethylene group, a propylene group, and a
butylene group. The carboxyl group in these groups may be linked as
a substituent group. In a case where the R group is a carboxyl
group, i.e., oxalic acid (HOOC--COOH), the oxalic acid may be
completely removed by degassing because oxalic acid is oxidatively
decomposed by electrochemical decomposition until carbon dioxide
gas is produced, and the decomposition by-product of the organic
acid does not remain in the battery.
In cases where the binder used in the positive electrode is a
polyvinylidenefluoride-type binder, e.g., polyvinylidenefluoride,
vinylidenefluoride-hexafluoropropylene copolymer, and
vinylidenefluoride-tetrafluoroethylene copolymer, it is desirable
that an effect achieved from the organic acid is to prevent
gelation of the positive electrode slurry including the
polyvinylidenefluoride-type binder. With regard to an additive
amount of the organic acid, while there is a trade-off relationship
between a gelation prevention effect and a reduction in the
previously mentioned battery charge/discharge efficiency resulting
from the organic acid, the trade-off relationship may be solved by
decomposition of the organic acid according to the present
description and degas of the organic acid outside the covering.
Accordingly, even more organic acid may be added and a more
effective gelation prevention effect may be obtained.
The negative electrode plate 42 constitutes the negative electrode
active material layer 42b, 42c disposed on both sides of the
rectangular-shaped negative electrode collector 42a that has
substantially the same measurements as the positive electrode
collector 41a. The negative electrode collector 42a is composed of
an electrochemically stabilized metal foil, e.g., a nickel foil, a
copper foil, a stainless steel foil, or an iron foil.
The negative electrode active material layer 42b, 42c is formed by
coating, drying and rolling a negative electrode slurry formed by
mixing the negative electrode active material sealing or emitting a
lithium ion of the positive electrode active material, e.g., an
amorphous carbon, a non-graphitizable carbon, a graphitizable
carbon, or a graphite, the binder, and the organic solvent
exemplified by N-methyl-2-pyrrolidone on a main surface of the
negative electrode collector 42a. An organic acid similar that used
in the positive electrode slurry may also be added during
preparation of the negative electrode slurry.
In cases where the binder used in the negative electrode is a
polyvinylidenefluoride type binder, e.g., polyvinylidenefluoride,
vinylidenefluoride-hexafluoropropylene copolymer, and
vinylidenefluoride-tetrafluoroethylene copolymer, it is desirable
that an effect achieved from the organic acid is further
stabilization of the binder on the negative electrode collector.
Specifically, a known organic acid may be exemplified, so long as
such an organic acid aims to improve adhesion of the binder and the
negative electrode. With regard to an additive amount of the
organic acid, while there is a trade-off relationship between a
binder stabilization effect and a reduction in the previously
mentioned battery charge/discharge efficiency resulting from the
organic acid, the trade-off relationship may be solved by
decomposition of the organic acid and degas of the organic acid
outside the covering as described in the present description.
Accordingly, even more organic acid may be added and a more
effective binder stabilization effect may be obtained.
A portion of an edge of a length-wise direction of the negative
electrode collector 42a extends as an extension that lacks the
negative electrode active material layer 42b, 42c, as shown in FIG.
1. The tip of the negative electrode collector 42a is connected to
a negative electrode terminal 3. Similarly, a portion of an edge of
a length-wise direction of the positive electrode collector 41a
extends as an extension that lacks the positive electrode active
material layer 41b, 41c. The tip of the positive electrode
collector 41a is connected to a positive electrode terminal 2.
The negative electrode terminal 2 and the negative electrode
terminal 3 protrude out to an exterior via a connecting surface of
the laminate film during heat-sealing of the laminate film of the
covering 5. In the Example of FIG. 2, while the positive electrode
terminal 2 is disposed at a first edge and the negative electrode
terminal 3 is disposed at a second edge, it is also possible that
the positive electrode terminal 2 and the negative electrode
terminal 3 may both be aligned and disposed on the same edge.
The separator 43 functions to prevent a short circuit between the
positive electrode plate 41 and the negative electrode plate 42,
while simultaneously storing electrolytes. The separator 43 is
composed of a microporous membrane formed of a polyolefin or the
like, e.g., polyethylene (PE) or polypropylene (PP). The polyolefin
or the like monolayer is not particularly limited as the separator
43, and thus a three-layered configuration sandwiching a
polypropylene membrane between two polyethylene membranes or a
laminated polyolefin microporous membrane and an organic nonwoven
fabric or the like, may be employed.
The nonaqueous electrolyte solution is not particularly limited,
and thus any known nonaqueous electrolyte solution may be used that
is typically employed in a lithium ion secondary battery, e.g., a
nonaqueous electrolyte solution having a lithium salt dissolved in
an organic solvent.
A known aprotic organic solvent may be employed as the organic
solvent of the nonaqueous electrolyte solution. For example,
ethylene carbonate, propylene carbonate, dimethylcarbonate,
diethylcarbonate, ethylmethyl carbonate, dimethylsulfoxide,
sulfolane, .gamma.-butyrolactone, 1,2-dimethoxyethane,
N,N-dimethylformamide, tetrahydrofuran, 1,3-dioxolane, 2-methyl
tetrahydrofuran, and diethylether may be exemplified as the aprotic
organic solvent. The above exemplified aprotic organic solvent may
be employed alone or in combinations of one or more.
For example, LiClO.sub.4, LiBF.sub.4, LiPF.sub.6, LiAsF.sub.6,
LiAlCl.sub.4, and Li(CF.sub.3SO.sub.2).sub.2N may be exemplified as
the lithium salt of the nonaqueous electrolyte solution. The above
exemplified lithium salt of the nonaqueous electrolyte solution may
be employed alone or in combinations of one or more.
In the method of manufacturing of the film-covered battery 1, the
nonaqueous electrolyte solution is injected into the covering 5
that includes the power generating element 4, and the organic acid
is decomposed in the nonaqueous electrolyte solution as a result of
an application of an electrical charge of the power generating
element 4 until a voltage level is equal to or above a
decomposition voltage of the organic acid. In addition, the gas
that is produced by decomposition thereof is eliminated from the
power generating element 4. As previously mentioned, the organic
acid is eliminated from the nonaqueous electrolyte solution.
Hereinafter, an example of a specific method of manufacturing the
film-covered battery 1 will be explained.
First, the negative electrode plate 42, the separator 43, the
positive electrode plate 41, the separator 43, and the negative
electrode plate 42 are sequentially laminated, and the power
generating element 4 is configured to attach to the positive
electrode terminal 2 and the negative electrode terminal 3 by
ultrasonic welding or the like. Then, the power generating element
4 is covered by the covering 5 and the openings of three edges of
the covering are heat-sealed. Next, the nonaqueous electrolyte
solution fills the inside of the power generating element 4 by
injection into covering 5 through a non-heat-sealed opening of the
edge. Thereafter, the covering 5 is tightly sealed by heat-sealing
the non-heat-sealed opening of the edge.
Second, an initial electrical charge is adjusted up to a
predetermined voltage level with respect to the power generating
element 4. The organic acid included in the nonaqueous electrolyte
solution is gasified by electrical charging. For example, in a case
where the organic acid is oxalic acid, oxidative decomposition
proceeds until carbon dioxide is produced. Next, as shown in FIG.
2, the covering 5 is cut at a boundary of a cut portion 6 along one
edge of the covering 5, from which the positive electrode terminal
and the negative electrode terminal 3 are not led out. The gas that
is produced is degassed from the covering 5 via an opening of the
cut portion 6. So long as the opening of the cut portion 6 is
re-heat-sealed after degassing, the film-covered battery 1 that has
the power generating element 4 tightly sealed inside the covering 5
will be complete. The opening of the cut portion 6 may be
heat-sealed as is by depressurizing an ambient environment of the
covering 5. It is preferable that the method employs a vacuum
sealing device.
Described in further detail, an oxalic acid may be eluted into a
nonaqueous electrolyte solution in cases where employing the oxalic
acid ((COOH).sub.2) as the organic acid at the time of preparation
of the slurry of the positive electrode active material layer 41b,
41c. A standard oxidation-reduction potential of a standard
hydrogen electrode of oxalic acid is -0.475 V. On the other hand,
the standard electrode potential of LiMn.sub.2O.sub.4 positive
electrode active material is 1.00 V, and the standard electrode
potential of LiNiO.sub.2 positive electrode active material is 0.80
V. Accordingly, the oxalic acid included in the nonaqueous
electrolyte solution is oxidatively decomposed until carbon dioxide
is produced, so long as the abovementioned initial electrical
charge voltage level is present. The carbon dioxide that is
produced primarily accumulates in the covering 5.
Next, the covering 5 is cut as previously mentioned, the carbon
dioxide is degassed from the opening of the cut portion 6 of the
covering 5, and the covering 5 is tightly sealed by re-heat-sealing
the opening of the cut portion 6, to thereby complete the
film-covered battery 1.
The gas that is produced in the covering 5 as a result of
depressurization of the ambient environment of the covering 5 by a
vacuum sealing device, such as previously described, at the time
that the cut portion 6 is formed, is immediately degassed, and the
cut portion 6 is heat-sealed as is.
Although the covering 5 is tightly sealed at the time of electrical
charging in the above example, the gas that is produced may be
degassed to an exterior of the covering during electrical charging
by performing electrical charging without sealing the injection
solution opening after injection of the injection solution or by
creating an opening in the temporarily sealed up covering 5 before
electrical charging. Even in the above cases, sealing of the
opening of the cut portion 6 may be accomplished by heat-sealing
the covering 5 under lower pressure using a vacuum chamber
including a heat-sealing mechanism.
Because the organic acid included in the nonaqueous electrolyte
solution may be eliminated according to a method of manufacturing
the film-covered battery 1, such as that described above, a lithium
ion secondary battery having enhanced charge/discharge efficiency
at the time of shipment may be obtained.
EXAMPLES
Hereinafter, examples of the present invention will be
described.
Example 1
A positive electrode slurry was obtained by measuring
LiMn.sub.2O.sub.4 as the positive electrode active material A,
oxalic acid as the organic acid B, and polyvinylidenefluoride as
the binder C at a weight ratio of A:B:C=95.9:0.1:4, and A, B, and C
were mixed with N-methyl-pyrrolidone as the organic solvent. Next,
a positive electrode formed by coating and drying the above
positive electrode slurry, such that the positive electrode has a
20 .mu.m positive electrode membrane thickness. The positive
electrode was stored in the covering including: a negative
electrode, a separator, and a laminate film. The nonaqueous
electrolyte solution was injected into the covering. Two batteries
were prepared by the above-described method. A first battery among
two batteries was electrically charged to 4V and then degassed. As
a specific degassing method, a cut portion 6 was formed in the
covering 5 as shown in FIG. 2, a vacuum sealing device was used
such that the surrounding area was in a reduced pressure
environment, and an opening in the cut portion 6 was heat-sealed as
it is. Then, the film-covered battery 1 was taken apart, and the
positive electrode fragment was cut out. A residue in the binder
was extracted while polyvinylidenefluoride was completely dissolved
by immersing the positive electrode fragment into
N-methylpyrrolidene after washing with diethyl carbonate, and the
amount of oxalic acid that was contained in the binder of the
positive electrode was measured. The amount of oxalic acid included
per unit weight of the positive electrode active material was one
third of an initial included amount. On the other hand, a hole was
created in a portion of the covering 5 of the battery 1 that was
not electrically charged, a little amount of the nonaqueous
electrolyte solution in the battery 1 was sampled through the hole,
and the concentration of the oxalic acid in the sampled solution
was measured. The dissolved amount of oxalic acid (total amount)
calculated by multiplying the injection amount in the battery and
the measured concentration value was two thirds of the total amount
of the oxalic acid prepared in the positive electrode. As a result,
two thirds of the total amount of the oxalic acid prepared in the
positive electrode before electrical charging was eluted into the
nonaqueous electrolyte solution. However, the oxalic acid was
determined to be absent from the nonaqueous electrolyte solution in
the battery after electrical charging and degassing.
Example 2
With the exception of forming the positive electrode by coating and
drying the positive electrode slurry, such that the positive
electrode had an 80 .mu.m positive electrode membrane thickness,
the two film-covered batteries of Example 2 were produced with the
positive electrode active material, the organic acid, and the
binder at a mixing ratio similar to that of Example 1. Degassing
from one of the two batteries was performed after electrical
charging until a voltage level similar to that of Example 1 was
achieved. Next, the battery was taken apart by a method similar to
that described in Example 1, a residue was extracted, and an amount
of oxalic acid was determined. The amount of the oxalic acid was
one half of the initial included amount. Even in the present
example, there was no trace of the oxalic acid in the nonaqueous
electrolyte solution in the battery after the degassing process. In
a case where the dissolved amount of the oxalic acid in another
electrolyte solution that was not electrically charged was also
measured in a manner similar to that described in example 1, one
half of the total initial amount of oxalic acid in the positive
electrode was measured. As a result, one half of the total initial
amount of the oxalic acid in the positive electrode before
electrical charging was eluted into the nonaqueous electrolyte
solution, and the oxalic acid was determined to be absent from the
nonaqueous electrolyte solution after electrical charging and
degassing.
Even in the batteries of Example 1 or 2, it is thought that the
oxalic acid was eluted from the electrode into the nonaqueous
electrolyte solution, the oxalic acid was oxidatively decomposed
until carbon dioxide was produced by application of an electric
charge thereafter, and the carbon dioxide gas was eliminated by
degassing.
Moreover, as a result of the above, a solution has been suggested,
in which the organic acid included in a nonaqueous electrolyte
solution is oxidatively decomposed until carbon dioxide is produced
and the organic acid is further eliminated to the covering in a
battery manufacturing process, the disadvantages resulting from an
oxidation-reduction reaction contributing to the oxidative
decomposition of the organic acid in the process of electrical
charging after shipment or an unwanted electrochemical reaction of
a re-dissolved molecule at the electrode surface by a gas resulting
from organic acid decomposition are eliminated, and a reduction in
charge/discharge efficiency of a battery is canceled as a result of
the reaction.
While preferred embodiments of the present invention have been
described and illustrated above, it is to be understood that they
are exemplary of the invention and are not to be considered to be
limiting. Additions, omissions, substitutions, and other
modifications can be made thereto without departing from the spirit
or scope of the present description. Accordingly, the present
description is not to be considered to be limited by the foregoing
description and is only limited by the scope of the appended
claims.
While a laminated lithium ion battery is specifically exemplified
in the abovementioned embodiments, various modifications may be
applied to the present description, e.g., a circular
cylinder-shaped battery, a coin-shaped battery, card-shaped
battery, a plate-shaped battery, an elliptic-shaped battery, a
square-shaped battery, and a button-shaped battery.
Moreover, while the organic acid was added during preparation of
the positive electrode slurry in the above examples, it is thought
that the result would be the same as that obtained in Examples 1
and 2 even in case where the organic acid was added during the
preparation of the negative electrode slurry.
REFERENCE SIGNS LIST
1 Film-covered battery (Nonaqueous electrolyte battery); 2 Positive
electrode terminal; 3 Negative electrode terminal; 4 Power
generating element; 5 Covering; 6 Cut portion; 41 Positive
electrode plate; 42 Negative electrode plate; and 43 Separator.
CITATION LIST
Patent Literature
Patent Literature 1: JP-A H-10-74521.
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